the government are tracking the attacks, working to keep them from becoming financial nightmares. abc's gene your justice correspondent pierre thomas starts us off. >> reporter: tonight, the financial and banking industry is on high alert as a massive cyber attack remains under way. potentially millions of customers trying bank online this past week blocked. among the targets, bank of america, pnc, and wells fargo. >> there is an elevated level of threat. the treat level is now high. >> reporter: sources tell abc news it is a denial of service attack, where hackers from the middle east have secretly commandeered thousands of computers worldwide. those computers, or zombies, have overwhelmed bank websites with a barrage of electronic traffic. different banks have been targeted different days. today was pnc's turn. we tried for three hours to get on pnc's website, but we couldn't get through. on facebook today, frustrated customers. cynthia wrote, "trying to pay bills. this is ridiculous." stacy posted, "hopefully it can be up soon. never realized how dependent i am on it." a group of hackers calli